1. Field of the Invention
The present invention relates to an electrophotographic image forming apparatus, and particularly to an image forming apparatus having a developer collecting section that collects developer containing deteriorated carrier or used developer in image formation (hereinafter referred to as waste developer).
2. Description of Related Art
In general, an image forming apparatus using an electrophotographic process technology (such as a printer, a copier, or a facsimile machine) irradiates (exposes) a charged photoconductor with (to) laser light based on image data to form an electrostatic latent image on the surface of the photoconductor. Toner is then supplied from a developing device to the photoconductor (image bearing member) bearing the electrostatic latent image, so that the electrostatic latent image is visualized as a toner image. The toner image is transferred to a sheet directly, or indirectly via an intermediate transfer belt, and fixed through heating and pressurization to form an image on the sheet.
Many image forming apparatuses employ a trickle development system. In the trickle development system, developer is regularly replaced by adding new developer (toner and carrier) while discharging developer (waste developer) containing deteriorated carrier. The waste developer discharged from developing devices in the trickle development system is all collected, for example in a collecting bottle through a developer collecting duct.
FIG. 1 illustrates developing devices and a developer collecting duct in a vertical tandem type image forming apparatus as viewed from the base end side (the side opposite to the side on which photoconductors are located) in the X direction. FIG. 2 illustrates the developing devices and the developer collecting duct in the vertical tandem type image forming apparatus as viewed from the base end side in the Y direction. FIG. 3 is a sectional view along a line A-A in FIG. 1. In FIGS. 1 to 3, the X axis represents the horizontal direction, the Z axis represents the vertical direction, and the Y axis represents a direction orthogonal to the X and Z axes (the direction of the axis of an agitating/conveying member).
As illustrated in FIGS. 1 and 2, the vertical tandem type image forming apparatus includes multiple developing devices (here, four developing devices for Y (yellow), M (magenta), C (cyan), and K (black)) 412Y, 412M, 412C, and 412K disposed in tiers in the vertical direction (Z direction). Developing devices 412Y, 412M, 412C, and 412K are treated as individual units and detachably attached to the body of the image forming apparatus. For example, developing devices 412Y, 412M, 412C, and 412K are mounted on a process carriage (not shown) and collectively attached to the body of the image forming apparatus. One end (on the base end side in the Y direction, i.e., the left side in FIG. 1) of each of developing devices 412Y, 412M, 412C, and 412K is coupled to developer collecting duct 170 linearly disposed in the vertical direction. The other end (on the tip end side in the Y direction, i.e., the right side in FIG. 1) is coupled to a power source (not shown), such as a driving motor, via a power transmission mechanism (not shown).
Specifically, as illustrated in FIG. 2, developer collecting duct 170 is provided with coupling portions 171Y, 171M, 171C, and 171K that accommodate and support the one end of respective developing devices 412Y, 412M, 412C, and 412K. Duct portions between adjacent upper and lower coupling portions, i.e., coupling portions 171Y and 171M, coupling portions 171M and 171C, and coupling portions 171C and 171K, are intermediate ducts 172.
As shown in FIG. 3, the one end of each of developing devices 412M and 412C is provided with pipe-like engaging portions 87M and 87C that house part of an agitating/conveying member (a developer conveying screw, not shown) and have developer outlets 89M and 89C, respectively. When engaging portions 87M and 87C are inserted into coupling portions 171M and 171C to attach developing devices 412M and 412C to developer collecting duct 170, developer outlets 89M and 89C are located inside developer collecting duct 170. Similarly, other developing devices 412Y and 412K are also coupled to developer collecting duct 170.
Unfortunately, coupling multiple developing devices 412Y, 412M, 412C, and 412K in tiers to developer collecting duct 170 as described above poses the following problem.
As illustrated in FIG. 3, engaging portions 87M and 87C of second and subsequent developing devices 412M and 412C are exposed to the inside of developer collecting duct 170. This causes waste developer T flowing from above to hit engaging portions 87M and 87C. Although engaging portions 87M and 87C of developing devices 412M and 412C are formed like a pipe in order to avoid accumulation of waste developer T, it is difficult to prevent accumulation of waste developer T over time. This also applies to fourth developing device 412K.
Waste developer T accumulated on engaging portions 87M and 87C may be scattered when developing devices 412Y, 412M, 412C, and 412K are detached during the time such as maintenance operation. The scattered waste developer may spill on, e.g., a sheet feeding path, causing poor images.
Such scattering of the waste developer may also occur in the case in which multi-tier cleaning devices for cleaning toner remaining on photoconductor drums are coupled to the developer collecting duct. That is, the above problem occurs in the case in which components that discharge waste developer (hereinafter referred to as developer discharging sections), such as developing devices or cleaning devices, are coupled in tiers to a developer collecting duct.
Techniques for preventing scattering of waste developer during maintenance operation include Japanese Patent Application Laid-Open Nos. 2009-103870 (PTL 1) and 2000-275975 (PTL 2), for example. PTL 1 and 2 disclose techniques for preventing scattering of waste developer using a receiver to receive the waste developer spilling from, e.g., developing devices. The techniques described in PTL 1 and 2, however, do not prevent the scattering itself of the waste developer and therefore are insufficient as preventive measures.